Purchased with the assistance of the National Heritage
Memorial Fund, The Art Fund (with a contribution from the Wolfson
collection) and the British Museum Friends

PE 2008,8017.1

Room 40: Medieval Europe

Astrolabe quadrant from Canterbury

Canterbury, England
Probably AD 1388

An extremely rare astronomical instrument from
medieval Canterbury

This extremely rare instrument is likely to
have belonged to a travelling scholar who may have lost it whilst
in Canterbury – maybe on pilgrimage. It remained in the ground
undisturbed until it was discovered in 2005 during an excavation at
the House of St Agnes in St Dunstan's Street.

Astrolabe quadrants are amongst the most
sophisticated instruments ever made before the invention of the
modern computer. They combine the mathematical and astronomical
features of an astrolabe with a much smaller size. They were thus
an extremely handy tool for their owners enabling them to establish
the time of day and to carry out a range of calculations based on
the position of the sun, such as the length of day. The side
of the quadrant with the rotating disc, called a volvelle, has
tables that enable the user to calculate the date of Easter. This
is very important as this prominent Christian feast is not fixed in
the calendar and its date changes every year. The wings of the
rotating eagle correlate the relevant data.

Astrolabe quadrants are extremely rare and
fewer than 10 medieval examples have been recorded. The
instrument was first described in the West by Jacob ben Machir ibn
Tibbon of Montpellier (about 1236-1305). He was a member of a
family that originated from Granada who was renowned for
translations from Arabic into Hebrew. Astrolabe quadrants are thus
uniquely placed to explain the link between the Islamic World and
Christian Europe and the role of Jewish scholars.

Examination of the scales on the instrument allows us to date
the astrolabe quadrant to 1388 and to firmly place its origins in
England. This makes the Canterbury quadrant the only example of
certain English origin. It is also the first ever occurrence of
such an instrument having been found during an archaeological dig –
scientific instruments are generally handed down from generation to
generation or found in attics, they are hardly ever found in the
ground.